Releasing natural variation in bread wheat by modulating meiotic crossovers

In bread wheat, important agronomical traits are distributed along chromosomes. Traditionally, plant breeders cross high yielding parental lines and then select for progeny in subsequent generations that carry desirable attributes whist removing undesirable traits. However, the process of 'gene-shuffling' (meiotic recombination) is non-random and skewed towards the ends of the chromosomes. Therefore, desirable traits are often transmitted as a block together with undesirable traits. This is analogous to dealing a deck of cards where a significant proportion of the cards are tethered by an elastic band. In this case a desirable hand cannot be achieved until the elastic band is severed and the cards are able to segregate freely. In this proposal we aim to understand why desirable and undesirable traits in bread wheat are often tethered together, so that we can break this bond, and release the full potential of available natural variation. Then, we aim to modulate this process so that the plant breeder can decide which traits can be 'dealt' together in the same variety. This unlocking of wheat's natural variation will lead to the production, via classical plant breeding, of superior varieties with favourable agronomic traits such as increased yield and improved nutrient acquisition.

To provide direct evidence that our research has application we will work with two of the UK's largest wheat breeders KWS and RAGT to target chromosomal regions, which are known to be transmitted as blocks. We will show that by using novel procedures, we can increase the amount of recombination in these blocks. Increasing the amount of recombination in any of these regions will enable breeders to generate new gene combinations which will lead to new varieties with, for instance, increased protein content or pathogen resistance. Further down the breeder's pipeline our research will directly translate to new varieties with superior characteristics that will help maintain farm incomes and improve sustainability of the UK arable and milling industries. In addition high yielding varieties will reduce dependence on imported grain and associated transport and environmental costs and improved pipelines for the generation of new UK varieties that will enhance reliability and competitiveness in overseas markets.

Meiotic recombination generates new alleles and new allelic combinations. Together with the ability of the wheat breeder to select desirable traits, the formation of new alleles and new allelic combinations determines the rate at which improved varieties are generated and they determine the extent of genetic gain. The products of recombination can be classified as being the result of crossovers (COs) or gene conversion. While both result in the formation of new alleles, CO's are essential for the formation of new allelic combinations. Unfortunately, in many species, COs are restricted in number (in wheat there are 1-3 per chromosome pair) and they are skewed in distribution to regions near the ends of chromosomes. As a result an estimated 30-50% of genes reside in recombination 'cold' regions. This creates the problem of linkage-drag in the cold centromere-proximal and interstitial regions where undesirable variation cannot be separated from useful traits. In effect, these regions become inaccessible to researchers and breeders alike. Thus, it is essential that we develop methods to manipulate the frequency and distribution of COs in species such as bread wheat and therefore aid the breeders in the generation of novel allelic combinations.

The aim of our five year work programme is to build upon our recent studies, and identify and modify the factors controlling CO frequency and distribution during meiosis via a range of complementary genetic and cytogenetic approaches. This knowledge will be used to manipulate CO formation in wheat, using synthetic approaches and targeting recombination using both a transgenic and non-transgenic approach.

Development of a set of tools and procedures which can be employed to manipulate both the rate and location of COs would revolutionise wheat breeding and they would lead to the rapid developments of a range of elite lines derived from novel germplasm.

Recombination is important to the UK wheat harvest because recombination drives plant breeding. The generation, selection and characterisation of new allelic combinations are essential if wheat breeders are to develop new varieties with superior traits. Unfortunately, plant breeders have no control as to where recombination occurs and therefore regions with little or no recombination are effectively excluded from the breeding process. Genes in areas devoid of recombination generate few novel allele combinations and therefore have a propensity to become fixed within breeding populations. Breaking such linkage blocks is a significant target for wheat breeders, and would unlock a wealth of untapped genetic variation. Thus, research that leads to such 'breakage' will have a dramatic economic impact on the breeding industry, farmers and society, who consume the wheat crop.

Social impact over the timescale of the project will be achieved by dissemination of the results through peer reviewed journal publication as well as oral and poster presentations at national and international scientific conferences. Information generated by the program will be made available via CerealsDB, which has recently been funded by the BBSRC until at least 2018. The importance of the project will be highlighted during university open days as well as outreach collaborations such as the NIAB Innovation Farm. The economic impact over the timescale of the project will include benefits to the suppliers of scientific materials in the UK. The main benefits to the UK economy will come at the latter stages of the project and when outputs are translated into novel elite varieties.

In the BBSRC 5-year wheat research strategy point 37 describes the 'need for succession planning and new blood', as there is a risk that as senior wheat researchers approach retirement age there are few obvious successors to cover the broad spectrum of areas encompassing wheat research. A sustainable plan for maintaining and augmenting wheat research capability is required to ensure a continued stream of innovation in the sector and supply of key skills to industry. Our project will take advantage of 1. The molecular and genetic experience in wheat from the PI Prof Edwards and co-investigator Dr Uauy and 2. The molecular and cytogenetic skills of co-investigator's Prof Franklin and Dr's Higgins, Henderson and Sanchez-Moran, to train the next generation of wheat geneticists/molecular cytogeneticists, at the post-graduate and post-doctoral level, in a range of skills and knowledge from the model plant Arabidopsis to wheat and vice versa.

Who will benefit from the increased skills and capacity? 1. Farmers, plant breeders, millers/bakers: Establishing procedures to generate new combinations for key genomic regions conferring, for instance, drought or insect resistance will enable wheat breeders to generate and select improved lines from elite UK germplasm. When translated to new varieties with superior characteristics this will help maintain farm incomes and improve sustainability of the UK arable and milling industries. In addition this will reduce dependence on imported grain and associated transport and environmental costs. Improved pipelines for the generation of new UK varieties will enhance reliability and competitiveness in overseas markets. 2. Scientists and plant breeders: Identification of biological processes linked to recombination will have a major impact on UK researchers who work with UK plant breeders to generate novel lines carrying a number of useful traits.